The experimental alloy powders of 1% Mg treated Al-8Fe-1.8V-8Si were obtained by air atomization. The screen analysis of powders was made by sieves with meshes ranging from +90µ / m, +63µ / m, +53µ / m, +45µ / m, +38µ / m to -38µ / m.
Unreinforced and TiC particulate reinforced specimens were produced by hot dynamic consolidation which is known as hot swaging. Powders were canned into pure aluminium tubes of about 10cm length and 2.2cm diameter. Single action and double action cold pressing were applied to some of the specimens before hot dynamic compaction and some specimens of canned loose powder were also processed. The diameters of the hot compacts were decreased in a two step process by swaging machine (rotary dynamic compaction). During the first step, after canning, compacts had been held at 480° / C for 1 hour and swaged, thus the diameter decreased from 2.2 cm to 1.97cm. Secondly, the compacts were reheated to 480º / C and held for 1 hour and further swaged to obtain a diameter decrease from 1.97cm to 1.54cm.
Generally, the microstructures of the hot dynamic compacted specimens were homogeneous except the specimens produced by using -63 µ / m +53 µ / m powder size fraction. By SEM study, a vanadium free cross like AlFeSi phase was observed near the outer regions of the specimen. No considerable coarsening of the dispersoids was observed after hot dynamic compaction of +63 µ / m size powder. For -90µ / m +63µ / m size powders, maximum flexural strength values obtained by three point bending test increased by addition of 10% TiC to from 152 MPa to 285 MPa at double pressed condition and from 76MPa to 190MPa at loose powder canning condition. By hardness tests, it was observed that hardness values were inversely proportional to powder size and increased from 107 BHN to 147 BHN for corresponding powder size range of +90µ / m to -38µ / m. Porosity values obtained by Archimedes principle for single pressing varied between 0.03 % and 1.10% for corresponding size range of +38µ / m to +90µ / m. No considerable porosity was detected for double pressing. Porosity values of canned loose powder were between 3% and 10% for the range of +38 µ / m- +45 µ / m. By X-Ray analysis, it was revealed that Mg2Si reaction did not form after artificial aging of specimens up to 8 hours at 190° / C. Also, x-ray analysis of individual powders and specimens obtained by hot dynamic compaction of the same powder showed that / after hot dynamic compaction, the alloy powders were stable and no new phase formation was detected for +63µ / m size. DSC examination of the specimens produced from +90µ / m, +63µ / m, +53µ / m, -38µ / m powder confirmed the microstructure stability up to the melting temperature. Melting temperature was detected to be in the range of 560° / C-575° / C by DSC.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12606070/index.pdf |
| Date | 01 May 2005 |
| Creators | Kotan, Sevkiye Ezgi |
| Contributors | Kalkanli, Ali |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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